Multi-center validation of Catquest-9SF visual function questionnaire in Ontario, Canada.

ABSTRACT

PURPOSE: To investigate the psychometric performance and responsiveness of Catquest-9SF, a patient-reported questionnaire developed to evaluate visual function as related to daily tasks, in patients referred for cataract surgery in Ontario, Canada. METHODS: This is a pooled analysis on prospective data collected for previous projects. Subjects were recruited from three tertiary care centers in Peel region, Hamilton, and Toronto, Ontario, Canada. Catquest-9SF was administered pre-operative and post-operatively to patients with cataract. Psychometric properties, including category threshold order, infit/outfit, precision, unidimensionality, targeting, and differential item functioning were tested using Rasch analysis with Winsteps software (v.4.4.4) for Catquest-9SF. Responsiveness of questionnaire scores to cataract surgery was assessed. RESULTS: 934 patients (mean age = 71.6, 492[52.7%] female) completed the pre- and post-operative Catquest-9SF questionnaire. Catquest-9SF had ordered response thresholds, adequate precision (person separation index = 2.01, person reliability = 0.80), and confirmed unidimensionality. The infit range was 0.75-1.29 and the outfit range was 0.74-1.51, with one item ('satisfaction with vision') misfitting (outfit value = 1.51). There was mistargeting of -1.07 in pre-operative scores and mistargeting of -2.43 in both pre- and post-operative scores, meaning that tasks were relatively easy for respondent ability. There was no adverse differential item functioning. There was a mean 1.47 logit improvement in Catquest-9SF scores after cataract surgery (p<0.001). CONCLUSION: Catquest-9SF is a psychometrically robust questionnaire for assessment of visual function in patients with cataract in Ontario, Canada. It is also responsive to clinical improvement after cataract surgery.